1. Field of the Invention
The present invention relates to vibration-damping steel, and further relates to structural steel preferably used as members of welded structures, for example. More particularly, it pertains to steel which has excellent vibration-damping properties capable of suppressing vibrations and noise, weldability, toughness and excellent strength as well.
2. Description of the Related Art
Vibrations and the noise emanating from such vibrations have become a social problem in recent years. These vibrations include those caused by mechanical structures and heavy traffic on railways and bridges as well as those produced in facilities such as factories and work places, particularly when these are located near residential areas.
To solve such a problem, various techniques are employed, such as using sound absorbing or insulating materials, or vibration insulating materials, and increasing the stiffness of structures to avoid resonance. However, in reality, vibrations and their source are a very complex phenomenon. It is generally difficult to eliminate the causes of vibrations. Even though noise can be reduced to some extent at its source, a huge amount of investment is required.
Thus, much attention has been shifted to methods for imparting vibration-damping properties to the materials themselves which are used as structural members, thereby solving the problem of vibration and noise emanating from a structure.
Several types of steel having the vibration-damping properties mentioned above have been proposed.
For example, Japanese Patent Publication No. 60-26813 discloses a manufacturing method for a type of vibration-proof steel having a low yield point and coarse grain. This steel, however, cannot be used as structural members because of low strength and inferior toughness.
Japanese Unexamined Patent Publication No. 52-144317 discloses a type of vibration-proof steel containing Ti, Al and 3 to 40 wt. % of Cr (hereinafter all weight percentages are denoted simply by %); Japanese Patent Publication No. 57-181360 discloses a thick vibration-damping steel plate containing 1.5 to 9% of Al; and Japanese Unexamined Patent Publication No. 57-22981 discloses a type of vibration-damping steel containing 4 to 8% of Cr and 3 to 5% of Al.
These types of steel have inferior weldability and are lacking in toughness or vibration-damping properties, and are expensive since enormous amounts of alloy components are added.
In addition, Japanese Unexamined Patent Publication No. 3-1621 discloses 18-8 stainless steel having vibration-damping properties because of grain boundary oxidation. Such stainless steel also has inferior weldability and is not suitable for mass production.